Silicone oil droplets are often found in therapeutic protein products, especially in pre-filled syringes or double-chamber cartridges, deriving from the lubrication process of the packaging material. Silicone oil droplets are not considered harmful by themselves, but might induce protein adsorption and aggregation leading to enhanced immunogenicity.

In routine methods for subvisible particle analysis such as light obscuration, silicone oil droplets are also detected as particles and cannot be differentiated from proteinaceous particles.

To avoid misinterpretation of the product stability due to high particle numbers caused by silicone oil droplets and to investigate the root cause of particle contamination, a differentiation of silicone oil droplets from protein particles is crucial.